The present invention is applicable to all types of projectiles, missiles or the like which are shot out of a firing tube or launching tube and which rotate in their track. In particular, this invention can be used with so-called end-phase-controlled ammunition, that is projectiles which are fired in the conventional manner in a ballistic track to the immediate vicinity of the target where they receive a command for required correction. Due to the fact that the projectile is rotating in its track, its roll attitude must be determined when the command is executed. In the absence of roll attitude determining elements, an error is otherwise produced when the course correction is carried out.
It is already known from Swedish Patent 8801831-2 to determine the roll angle attitude with the aid of polarized electromagnetic radiation comprising a transmitter arranged to emit a polarized radiation in the direction of the projectile and a polarization-sensitive receiver arranged in the projectile. By allowing the emitted polarized radiation to comprise at least two mutually phase-locked radiation components with wavelength relations of 2:1 and/or multiples thereof and which are superimposed and form an asymmetric curve shape, the roll attitude of the projectile can be unambiguously determined.
The abovementioned arrangement presupposes that a transmitter is placed in connection with the launching place of the projectile and that the projectile is provided with a receiver antenna directed towards the back for receiving the emitted radiation.
The arrangement furthermore presupposes that two mutually phase-locked radiation components with different frequencies are sent out. This entails that both transmitter and receiver become relatively complicated in their construction.
It is also known from EP 0 341 772 to determine the roll angle attitude by providing the single carrier wave with a sinusoidal amplitude modulation for continuously transmitting information about the phase angle. Such a system has advantages through a simpler construction of the receiver section in the projectile. But it is also disclosed that it requires two antennas in the receiver with known mutual orientation.
From Swedish Patent Application 9001370-7, it is also already known to determine the roll angle attitude with the aid of partly a polarized sinusoidal radiation within the longwave band and partly a microwave radiation in the form of a pulse train where the pulses indicate that the long wave component is located at a certain phase angle, for example, the sinusoidal signal zero transition with positive derivative. The two radiation components are then detected in the grenade and supplied to a microprocessor system for evaluation.
The advantage of transferring the message about the phase angle only at certain times is that such a system becomes more interference-proof. The risk of detection becomes less, it is more difficult to calculate the frequency utilized for transmission from the short pulses and in this way to interfere with the transmission.
In such a system, one therefore depends on two radiation components, both a longwave component and a microwave component. A synchronization between transmitter and receiver is also necessary.